Member postings for old mart

Making a small screw I would use larger diameter stock and turn down the shank of the screw first. Then have a metal bush with a hole in it for the larger diameter to fit in against the face of the die to ensure squareness. I would screw it into the die rather than screwing the die onto the work. After the thread was finished, the head diameter and length could be carried out, together with any screwdriver slot. Hexagon flats would be easier to produce before cutting the head from the main stock.

Welcome to the forum Christopher, some excellent advice has been offered by members, especially about practicing, and if you have drawings, then start with the easer looking parts first. The hobby can be expensive, so some dedication is needed.

A split die can be opened up so a partial thread can be produced at the first pass which can have an advantage. The diestock bore needs to be slightly bigger than the die, or you will not be able to adjust the size. The steel used will vary in threadability enormously, and being to measure the diameter to at least 0.0005", 0.01mm is vital with such small diameters, a screw micrometer may be better to use than calipers. Use cutting oil on steel. Tracey Tools are very good suppliers.

Edited By old mart on 09/09/2022 20:02:41

Edited By old mart on 09/09/2022 20:04:07

The Taiwanese round column drill mill at the museum has a 500mm X axis travel, and when I decided to pair up the two 100mm Bison vises with keys to hold long work, it was found that the rear face of the table slot used by them had a 0.007" run from side to side. I managed to use the mill to skim the high spot out in 3 stages by swinging the head left and right. The error was mostly in the left hand third of the travel, so just touching with the side of a 12mm solid carbide cutter did most of the slot side. Now the error is better than 0.001" over the entire length. I have never bothered to check the other 3 slots.

Because of the small diameter of the nose of centre drills, the maximum speed available should be used, together with lubrication. The extended nose is there for a purpose, to make sure the flanks of a centre are making contact without the point touching. For drilling, a spot drill would be preferred, or I use a "centre" drill with a 90 degree flank rather then the 60 degree intended for using with a centre.

If the fault with the thread is confined to the external shoulders, I would stick it in the lathe using backgear and chase the thread with a round file of about 3/16" - 1/4" diameter. The lathe could also skim the 3/4" od of the thread, or a flat file could be used.

I would also investigate the cause of the burrs, they are not usual, most nuts are cast iron or bronze, mazak if an Atlas or Myford.

Edited By old mart on 09/09/2022 14:37:17

I did notice in the videos that the lever of the indicator didn't seem to be tangential to the spindle, that would give the best figures. Could you also mark the high spots and do a third test on the MT tool in the spindle taper.

It would be possible to have the journals built up with nickel plating or metal spray and then re machined true, the surfaces would have to be reduced in diameter by about 0.01" first. It might also be possible to find bearings with a slightly smaller bore, but that would depend mostly on how lucky you are.

We inherited a Tom Senior light vertical at the museum which had a much abused bed. It is the longer bed model and I determined that removing 1.5mm, about 1/16" would remove 90% of the damage. I bought two sets of 124 blocks on ebay, and was pleased to find that both sets matched exactly in all axes. The center tee slot had 4 evenly spaced holes drilled right through to take SHCS screws holding into tee nuts made to fit our other mill, one of the larger roung column drill mills. The blocks supported the TS bed on the other mill, but it had to be milled in 4 stages, repositioning each time. Then the inverted bed was rubbed by hand on the surface table which was covered with 120 paper held down with double sided tape. Only sheets from one packet were used, as different batched vary in thickness. The rubbing was done over several weeks and was very slow, and I decided to give up when there was just a shadow of milling marks left at the ends of the bed. How accurate is it ? If the head is trammed to 0.0005" or better with the bed in the central position, and then the tramming is checked at either extreme of travel, the ends are both 0.002" higher, this with a tramm about 10" swing. Good enough for our purposes. With an 18" straight edge, our longest, the top of the bed is better than 0.0002".

Would I do it again? I really don't know.

It would be worth checking machine shops and see if any would have a big enough mill to do your bed in one go. Measure the depth of the damage to see if all or part can be removed without compromising the bed.

Rather difficult to make in tool steel, but there might be another way. With an indexable external threading tool an an 8 ACME insert, the leadscrew could be cleaned up simply by chucking it up in sections with tailstock support, and letting the insert pull the saddle (carriage) along about 8" at a time before re positioning it.

I successfully added 4" of 8 ACME thread to the Tom Senior Xaxis leadscrew to allow fitting backlash adjustable nuts. After cutting the new thread, I had to cut the entire length to match the centre part which had some wear or the antibacklash would not have worked. It was done in several sections with as much tailstock, fixed and travelling steady support as I could manage. That leadscrew was twice the lathe centre length.

Your leadscrew could be deburred in short sections close to the chuck using any suitable lathe tool before running the threading insert along.

I would never use a solid die by choice to produce a new thread, I consider them as "die nuts" good only for running down a thread if it needs restoring. I always start with a split die opened up in the stock for the first pass and then close up and check the fit of the nut. Single pointing on the lathe is best, and using an internal threading bar behind the workpiece with the lathe in reverse, it is easy to cut the thread right up to a shoulder.

I would favour locking the saddle (carriage) and use a lever operated tool, it would also have much better feel.

I agree, Bernards bung would have prevented the distortion.

 There is nothing better than learning by your mistakes, I'm getting to the point where I remember the best way to do something after doing it the wrong way.

Edited By old mart on 06/09/2022 21:09:23

Another way would be to make two bearings, bore them and cut them in two with a hacksaw offset from the centre and then filing or milling the bigger one of each back to the centreline.

With a carbide grit coated hacksaw blade, the die could be made into a split die. Then it could be opened up slightly to produce a larger diameter thread.

Fizzy's leaded bronze sounds a good idea, I have never tried that.

I notice that 12 size unified is only 0.00275" smaller than 7/32", so if you can get a split die, the size could be matched pretty well.

You should check to see if the pulleys are in line and parallel before dismantling.

I have bought springs on ebay, there is an astounding range for sale.

I use one of Jason's collet plates to hold the mills er25 tooling in the smart & Brown lathe.

As long as the length of thread engagement of the drawbar in the tool is as long as possible, then a smart rap with a copper hammer after slackening off a couple of turns is acceptable.

I would have bored the centre last, holding it in external jaws. You are absolutely right in decscribing the distortion process.

By the way, on my monitor, the metal looks like steel, not brass.

Edited By old mart on 05/09/2022 14:43:22